This invention relates to a process for the removal of metal poisons or contaminants from a hydrocarbon conversion catalyst which has been contaminated with one or more metal poisons or contaminants by use in a high temperature catalytic conversion of hydrocarbon feedstocks containing such metals or contaminants. More particularly, this invention relates to an improved method for removing metal contaminants from a hydrocarbon conversion catalyst. The invention may be used as part of an overall metals-removal process employing a plurality of processing steps to remove a significant amount of one or more of nickel, vanadium, copper, and iron metals contained in a poisoned catalyst.
Catalytically promoted methods for the chemical conversion of hydrocarbons include cracking, hydrocracking, reforming, hydrodenitrogenation, hydrodesulfurization, etc. Such reactions generally are performed at elevated temperatures, for example, about 300.degree. to 1200.degree. F., more often 600.degree. to 1000.degree. F. Feedstocks to these processes comprise normally liquid and solid hydrocarbons which, at the temperature of the conversion reaction, are generally in the fluid, i.e., liquid or vapor state, and the products of the conversion usually are more valuable, lower boiling materials.
In particular, cracking of hydrocarbon feedstocks to produce hydrocarbons of preferred octane rating boiling in the gasoline range is widely practiced and uses a variety of solid oxide catalysts to give end products of fairly uniform composition. Cracking is ordinarily effected to produce gasoline as the most valuable product and is generally conducted at temperatures of about 750.degree. to 1100.degree. F., preferably about 850.degree. to 950.degree. F., at pressures up to about 2000 psig., preferably about atmospheric to 100 psig. and without substantial addition of free hydrogen to the system. In cracking, the feedstock is usually a petroleum hydrocarbon fraction such as straight run or recycle gas oils or other normally liquid hydrocarbons boiling about the gasoline range. Recently, low severity cracking conditions have been employed for heavily contaminated feedstocks such as crude or reduced crude where the conversion is not made directly to the most valuable, lower boiling products, i.e., gasoline boiling range products, but to intermediate type hydrocarbon conversion products which may be later refined to the more desirable, lower boiling, gasoline or fuel oil fractions. High severity cracking has also been practiced for the conversion of such feedstocks to light, normally gaseous hydrocarbons, such as ethane, propane or butane.
The present invention relates to the improvement of catalyst performance in hydrocarbon conversion where metal poisoning occurs. Although referred to as "metals," these catalyst contaminants may be present in the hydrocarbon feed in the form of free metals or relatively non-volatile metal compounds. It is, therefore, to be understood that the term "metal" as used herein refers to either form. Various petroleum stocks have been known to contain at least traces of many metals.
Some patents exemplifying some of the state of the art in this area are discussed hereinafter and the teachings of which are expressly incorporated herein by reference.
U.S. Pat. No. 2,668,798 (1954) of C. J. Plank discloses a process for overcoming poisonous affects of nickel contamination on the conversion efficiency of siliceous cracking catalysts by subjecting such catalysts to a mild acid treatment followed by a mild steam treatment. The acid used may be either a mineral acid such as sulfuric, nitric, hydrochloric, phosphoric and the like, or an organic acid such acetic, oxalic, tartaric and the like.
U.S. Pat. No. 3,122,497 (1964) of H. Erickson discloses a process to remove metal poisons from a synthetic gel hydrocarbon conversion catalyst. Metals to be removed are one or more of nickel, vanadium and iron. Nickel is especially removed in the process. The process disclosed involved sulfiding a regenerated catalyst and then converting sulfided components of the poison catalyst such a nickel sulfide to a volatile or water dispersible nickel compound. Among the methods for converting a sulfided component to water dispersible material is a liquid aqueous oxidizing medium, such as dilute hydrogen peroxide or hypochlorous acid water solutions, including sulfuric acid or nitric acid to reduce consumption of peroxide, aerated dilute nitric acid solutions in water, sodium peroxide in acid solutions such as chromic acid, solutions of manganates, permanganates, chlorites, chlorates, perchlorates, bromites, bromates, perbromates, iodites, iodates and periodates, bromine or iodine water, an aerated, ozonated or oxygenated water with or without acid. Not disclosed is the use of nitrate ions catalyzed by nitrite ions to oxidize sulfided components of a sulfided catalyst.
U.S. Pat. Nos. 3,122,510, 3,122,511 and 3,122,512 disclose a process for the removal from a solid oxide hydrocarbon conversion catalyst metals such as nickel, vanadium, and iron. The process involves regenerating a carbonaceous coated conversion catalyst which has been contaminated by metal contaminants such as nickel, vanadium, and iron followed by sulfidation and finally followed by a chlorination. Chloriding of the sulfided catalyst is carried out to convert sulfided metal contaminants to a water dispersible form.
U.S. Pat. No. 3,123,548 (1964) of J. E. Connor, Jr. discloses the use of a cation exchange resin in conjunction with an oxidation of a sulfided cracking catalyst. The sulfided catalyst is air oxidized to convert sulfided components to water dispersible forms of metal contaminants.
U.S. Pat. No. 3,146,188 (1964) of E. C. Gossett discloses a process for cracking a residual oil containing metallic impurities. Vis-breaking operating conditions are employed during the cracking process. The contaminated catalyst is disclosed to remove contaminating metals by, in one instance, converting a sulfide component to a water dispersible form.
U.S. Pat. No. 3,147,209 (1964) of H. Erickson discloses sulfiding a previously regenerated catalyst containing metal contaminants and contacting the sulfided catalyst with an oxygen-containing gas-steam mixture to convert any metal sulfides to water-dispersible materials.
U.S. Pat. No. 3,147,228 (1964) discloses various ways of carrying out a sequence, which consists of a regeneration to burn off carconaceous deposits from a conversion catalyst sulfiding such a regenerated catalyst and oxidizing the sulfided catalyst to convert metal sulfides to water dispersible form. The oxidation is preferably in an anhydrous condition meaning no separate liquid phase.
U.S. Pat. No. 3,150,072 (1964) of W. E. Watson discloses an aqueous phase oxidation of a sulfided catalyst employing an aerated dilute nitric acid solution in water.
U.S. Pat. No. 3,168,459 (1961) of A. D. Anderson et al. discloses an oxidation either in the aqueous phase or gas phase of a sulfided contaminated cracking catalysts to remove metal contaminants.
U.S. Pat. No. 3,182,011 (1965) of B. S. Friedman discloses an aqueous phase oxidation of a sulfided and previously regenerated cracking catalyst wherein peroxide oxidizing agents are used.
U.S. Pat. No. 3,252,981 (1966) of W. L. Disegna et al. discloses an improved method of oxidizing a regenerated catalyst to promote the removal of vanadium from a synthetic gel, silica-base cracking catalyst. The improvement involves adding an oxide of nitrogen to a molecular oxygen gas phase oxidation of a regenerated catalyst to promote vanadium removal.
A commercial catalyst demetallization process is disclosed in an article entitled "DeMet Improves FCC Yields" appearing in The Oil and Gas Journal of Aug. 27, 1962, pp. 92-96 and in an article entitled "The Demetallization of Cracking Catalysts" appearing in I & E C Product Research and Development, Vol. 2, pp. 328-332, December, 1963. This process while successful in accomplishing its intended purpose with the catalysts described encountered metal corrosion problems in conjunction with the chlorination reactions involved. In addition, this process utilizes a sulfidation pretreatment step which places in excess of 2.0 wt % sulfur on the catalyst. In subsequent steps, this sulfur as it is removed from the catalyst, can be converted to elemental sulfur which, in turn, can deposit in the reactor and transfer lines. These deposits can accumulate to excessive levels and lead to plugging of the reactor lines.
Nowhere is there disclosed in any of the cited prior art the use or the advantages from the use of a nitrite catalyzed nitrate oxidation in an aqueous phase of a sulfided cracking or chemical conversion catalyst.
Commercially used hydrocarbon cracking catalysts are the result of years of study and research into the nature of cracking catalysts. The cost of these catalysts frequently makes highly poisoned hydrocarbon feedstocks, even though they may be in plentiful supply, less desirable to use in cracking operations because of their tendency to deactivate valuable catalysts. These preferred catalysts, because of their composition, structure, porosity and other characteristics give optimum results in cracking. It is important, therefore, that removing poisoning metals from the catalyst does not substantially adversely affect the desired chemical and physical constitution of the catalyst. Although methods have been suggested in the past for removing poisoning metals from a catalyst which has been used for high temperature hydrocarbon conversions, the process of this invention is particularly effective to remove nickel while substantially maintaining the effectiveness and composition of the catalyst.
Solid oxide catalysts have long been recognized as useful in catalytically promoting the conversion of hydrocarbons. For hydrocarbon cracking processes carried out in the substantial absence of added free molecular hydrogen, suitable catalysts can include amorphous silica alumina catalysts which are usually activated or calcined predominately silica or silica-based, e.g., silica-alumina, silica-magnesia, silica-zirconia, etc., compositions in a state of slight hydration and containing small amounts of acidic oxide promoters in many instances. The oxide catalyst may contain a substantial amount of a gel or gelatinous precipitate comprising a major portion of silica and at least one other inorganic oxide material, such as alumina, zirconia, etc. These oxides may also contain small amounts of other inorganic materials. The use of wholly or partially synthetic gel or gelatinous catalyst, which are uniform and little damaged by high temperatures in treatment and regeneration is often preferable.
Also suitable are hydrocarbon cracking catalysts which include a catalytically effective amount of at least one natural or synthetic zeolite, e.g., crystalline alumino silicate. A preferred catalyst is one that includes at least one zeolite to provide a high activity catalyst. Suitable amounts of zeolite in the catalyst are in the range of about 1-75% by weight. Preferred are zeolite amounts of about 2-30% by weight of the total catalyst. Catalysts which can withstand the conditions of both hydrocarbon cracking and catalyst regeneration are suitable for use in the process of this invention. For example, a phosphate silica-alumina silicate composition is shown in U.S. Pat. No. 3,867,279, chrysotile catalysts are shown in U.S. Pat. No. 3,868,316, and a zeolite beta type of catalyst is shown in No. Re. 28,341. The catalyst may be only partially of synthetic material; for example, it may be made by the precipitation of silica-alumina on clay, such as kaolinite or halloysite. One such semi-synthetic catalyst contains about equal amounts of silica-alumina gel and clay.
The manufacture of synthetic gel catalyst is conventional, well known in the art and can be performed, for instance (1) by impregnating silica with alumina salts; (2) by direct combination of precipitated (or gelated) hydrated alumina and silica in appropriate proportions; or (3) by joint precipitation of alumina and silica from an aqueous solution of aluminum and silicon salts. Synthetic catalyst may be produced by a combination of hydrated silica with other hydrate bases as, for instance, zirconia, etc. These synthetic gel-type catalyst may be activated or calcined before use.
A particularly preferred catalyst contains a catalytically effective amount of a decationized zeolitic molecular sieve having less than 90% of the aluminum atoms associated with cations, a crystalline structure capable of internally absorbing benzene and a SiO.sub.2 to Al.sub.2 O.sub.3 molar ratio greater than 3. Such catalysts are illustrated in U.S. Pat. No. 3,236,761, the teachings of which are incorporated by reference herein.
The physical form of the catalyst is not critical to the present invention and may, for example, vary with the type of manipulative process in which it will be used. The catalyst may be used as a fixed bed or in a circulating system. In a fixed-bed process, a single reaction zone or a series of catalytic reaction zones may be used. If a series of reactors are used, one is usually on stream and others are in the process of cleaning, regeneration, etc. In circulating catalyst systems, such as those of the fluid bed or moving bed catalytic processes, catalyst moves through a reaction zone and then through a regeneration zone. In a fluid bed cracking process, gases are used to convey the catalyst and to keep it in the form of a dense turbulent bed which has no definite upper interface between the dense (solid) phase the suspended (gaseous) phase mixture of catalyst and gas. This type of processing requires the catalyst to be in the form of a fine powder, e.g., a major amount by weight of which being in a size range of about 20 to 150 microns. In other processes, e.g., moving bed catalytic cracking system, the catalyst can be in the form of macrosize particles such as spherical beads which are conveyed between the reaction zone and the catalyst regeneration zone. These beads may range in size up to about 1/2" in diameter. When fresh, the minimum size bead is preferably about 1/8". Other physical forms of catalyst such as tablets, extruded pellets, etc. can be used.
In this invention the hydrocarbon petroleum oils utilized as feedstock for a given conversion process may be of any desired type normally utilized in such hydrocarbon conversion operations. The feedstock may contain nickel, iron and/or vanadium as well as other metals. As indicated, the catalyst may be used to promote the desired hydrocarbon conversion by employing at least one fixed bed, moving bed or fluidized bed (dense or dilute phase) of such catalyst. Bottoms from hydrocarbon processes, (i.e., reduced crude and residuum stocks) are particularly highly contaminated with these metals and therefore rapidly poison catalysts used in converting bottoms to more valuable products. For example, a bottom may contain about 100-1500 ppm Ni, about 100-2500 ppm V and about 100-3000 ppm Fe. For typical operations, the catalytic cracking of the hydrocarbon feed would often result in a conversion of about 10 to 80% by volume of the feedstock into lower boiling, more valuable products.